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Abstract:

In a disk drive device, a magnetic recording disk is mounted on a hub. A
base rotatably supports the hub via a bearing unit. The base has a
ring-shaped wall that surrounds the bearing unit and that protrudes
towards the hub. A laminated core is fixed to the base. The laminated
core has a ring portion and twelve teeth that radially outwardly extend
from the ring portion. Coils are wound around the twelve teeth. The base
includes an increasing-thickness portion formed so that the less the
distance between a part of the increasing-thickness portion and the
ring-shaped wall is, the thicker the part of the increasing-thickness
portion becomes.

Claims:

1. A rotating device, comprising: a hub on which a recording disk is to
be mounted; a base rotatably supporting the hub via a bearing unit, the
base having a ring-shaped wallsurrounding portion that surrounds the
bearing unit and that protrudes towards the hub; a core fixed to the
base, the core having a ring portion and a plurality of teeth that
radially extend from the ring portion; and coils wound around the
plurality of teeth, wherein the base includes an increasing-thickness
portion formed so that the less the distance between a part of the
increasing-thickness portion and the ring-shaped wallsurrounding portion
is, the thicker the part of the increasing-thickness portion becomes.

2. The rotating device according to claim 1, wherein the coil is formed
so that the distance between the coil and the increasing-thickness
portion is greater than a predetermined distance.

3. The rotating device according to claim 1, wherein the coil has a
decreasing-thickness portion, the thickness of which decreases in
accordance with the profile of the increasing-thickness portion.

4. The rotating device according to claim 1, wherein the
increasing-thickness portion is formed so that the hub maintains a
predetermined height even if a test impact load of 1200 G is applied.

5. The rotating device according to claim 1, wherein the
increasing-thickness portion is formed so that the following equation is
satisfied: H ( x ) H 0 ≧ k ( x x 0 ) -
1.2 ( equation 1 ) ##EQU00004## where x is a distance
between a part of the increasing-thickness portion and a rotational axis
of the hub, x0 is a predetermined reference distance, H(x) is a
thickness of the increasing-thickness portion at the distance x, H0
is a predetermined reference thickness, and k is a predetermined
constant.

6. The rotating device according to claim 1, wherein the base has a
coil-facing portion arranged to be adjacent to the increasing-thickness
portion, which is located outside of the increasing-thickness portion in
a radial manner, and arranged to face the coil in the direction along the
rotational axis of the hub, and the portion of the hub that faces the
coil in the direction along the rotational axis of the hub is thicker
than the coil-facing portion.

7. The rotating device according to claim 1, wherein, when a coordinate
is defined along the rotational axis of the hub, the coordinate range of
the core at least partly overlaps the coordinate range of a portion where
the bearing unit touches the ring-shaped wall.

8. The rotating device according to claim 1, wherein the bearing unit is
formed so that the diameter of the portion where the bearing unit touches
the ring-shaped wallsurrounding portion is greater than the diameter of
another portion.

9. The rotating device according to claim 1, wherein the space on the
hub-side of the base is filled with a gas, which includes a predetermined
ratio of Helium, and a through hole is provided on the base, and a seal
member is provided along an edge of the through-hole on a surface of the
base opposite to the hub.

10. The rotating device according to claim 1, further comprising a
ring-shaped thrust ring, the center of which is along the rotational axis
of the hub, the ring-shaped thrust ring being fixed to the hub, and the
thrust ring has a substantially flat hub-facing surface that faces the
hub in the direction along the rotational axis of the hub, and a part of
the hub-facing surface is in contact with the hub and the other part,
when the hub rotates, suppresses the motion of the hub in the direction
along the rotational axis of the hub in cooperation with the bearing
unit.

11. The rotating device according to claim 10, wherein the thrust ring is
made of a material, the hardness of which substantially is equal to that
of the hub.

12. A rotating device, comprising: a hub on which a recording disk is to
be mounted; a base rotatably supporting the hub via a bearing unit; a
core fixed to the base, the core having a ring portion and a plurality of
teeth that radially extend from the ring portion; coils wound around the
plurality of teeth; a magnet fixed to the hub, the magnet being
magnetized for driving with a plurality of poles along the
circumferential direction and arranged to radially face the plurality of
teeth; and a suction plate facing the magnet in the direction along the
rotational axis of the hub, the suction plate being made of magnetic
material, wherein the suction plate has a ring portion and a plurality of
projecting portions that radially extend from the ring portion, and the
suction plate is fixed to the base by the plurality of projecting
portions being fixed to the base.

13. The rotating device according to claim 12, wherein the thickness of
the suction plate is greater than or equal to 0.1 mm and less than or
equal to 0.4 mm.

14. The rotating device according to claim 12, wherein the number of the
projecting portions of the suction plate is greater than or equal to 3
and less than or equal to 12.

15. The rotating device according to claim 12, wherein, when a coordinate
is defined along the rotational axis of the hub, the coordinate range of
the suction plate at least partly overlaps the coordinate range of the
hub.

16. A method for manufacturing a rotating device that has a fluid dynamic
bearing, comprising the steps of: providing the fluid dynamic bearing
without lubricant in a predetermined work space; creating a vacuum in the
work space; discharging the lubricant in a storage region of the fluid
dynamic bearing, the storage region storing the lubricant; introducing
the lubricant stored in the storage region into a region of the fluid
dynamic bearing where the lubricant is to be present, by restoring the
pressure of the work space; and measuring, with regard to the fluid
dynamic bearing with the introduced lubricant, a first height of the
fluid level of the lubricant in the direction along the rotational axis
under a first pressure different from the atmospheric pressure.

17. The method according to claim 16, further comprising the steps of:
measuring, with regard to the fluid dynamic bearing with the introduced
lubricant, a second height of the fluid level of the lubricant in the
direction along the rotational axis under a second pressure different
from the first pressure; and inspecting the fluid dynamic bearing with
the introduced lubricant based on the measured first height and the
measured second height.

18. The method according to claim 17, further comprising the step of:
removing, with regard to the fluid dynamic bearing with the introduced
lubricant, the fluid dynamic bearing if the difference between the
measured first height and the measured second height is greater than 50
μm.

19. The method according to claim 16, wherein the first pressure is less
than or equal to 100 Pa.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is based upon and claims the benefit of priority
from the prior Japanese Patent Application No. 2010-109459, filed on May
11, 2010, the entire content of which is incorporated herein by
reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a rotating device and a method for
manufacturing a rotating device.

[0004] 2. Description of the Related Art

[0005] Disk drive devices, such as hard disk drives, have become
miniaturized. The capacity of a disk drive device has also been
increased. Such disk drive devices have been installed in various types
of electronic devices. In particular, such disk drive devices have been
installed in portable electronic devices such as laptop computers or
portable music players. With regard to disk drive devices that are
installed in portable electronic devices, their impact resistance has
been required to be improved so that the disk drive devices can withstand
impacts, such as those due to dropping, compared with the case of
stationary electronic devices such as desk-top personal computers.

[0006] On the other hand, in general, portable electronic devices have
been required to be made thinner, smaller, and lighter. Therefore, disk
drive devices that are installed in portable electronic devices have also
been required to be made thinner, smaller, and lighter. However, it is
possible that the impact resistance decreases in the course of making the
disk drive devices thinner, smaller, and lighter. It can be said that
there is a trade-off imposed on the disk drive devices that are installed
in portable electronic devices.

[0007] For example, in the case where the disk drive device is used for a
desk-top PC, any impact applied to the disk drive device would be small,
and it would not be likely that the disk drive device malfunctions in
normal usage. However, in the case where the disk drive device is used
for portable electronic devices, the disk drive device may receive a
large impact such as those due to dropping. There would be many cases
where a large impact is applied to the disk drive device. Therefore,
there is a possibility that the disk drive device malfunctions in use
unless the disk drive device has considerable impact resistance.

[0008] In order to cope with this, the prior art installs a fluid dynamic
bearing unit (hereinafter referred to as "FDB") in a disk drive device as
disclosed in Japanese Patent Application Publication No. 2007-198555. In
this FDB, a flange portion is sandwiched between an extended portion of a
sleeve and the end surface of a housing. The flange portion is formed in
an inner cylindrical region. A lubricant is filled in between the flange
portion and the extended portion of the sleeve, and the lubricant is also
filled in between the flange portion and the end surface of the housing.

SUMMARY OF THE INVENTION

[0009] Under the above circumstances, the inventors of the present
invention encountered the following concern: as shown in Japanese Patent
Application Publication No. 2007-198555, for example, for a typical disk
drive device, the FDB is fixed to a base, and a hub is rotatably
supported with respect to the base by the FDB. A magnetic recording disk
is mounted on the hub and rotated. When acceleration due to an impact is
applied to such a disk drive device, a stress is applied near the center
of the base. The strength of the stress corresponds to the value given by
multiplying the acceleration due to the impact by sum of the masses of
the magnetic recording disk, the hub, the FDB, a core, and the coil. In
particular, this stress tends to concentrate at the root of an annular
wall portion of the base that upwardly protrudes and that supports the
FDB.

[0010] In order to maintain the impact resistance of the disk drive
device, the base has to withstand the stress that concentrates at the
root of the annular wall portion. Therefore, in prior art, it is
necessary to make the base thick enough to withstand this stress.
However, for the purpose of thinning the disk drive device, this
thickness may be a bottleneck.

[0011] The present invention addresses these disadvantages, and a general
purpose of one embodiment of the present invention is to provide a
rotating device that has good impact resistance.

[0012] An embodiment of the present invention relates to a rotating
device. The rotating device comprises: a hub on which a recording disk is
to be mounted; a base rotatably supporting the hub via a bearing unit,
the base having a ring-shaped wallsurrounding portion that surrounds the
bearing unit and that protrudes towards the hub; a core fixed to the
base, the core having a ring portion and a plurality of teeth that
radially extend from the ring portion; and coils wound around the
plurality of teeth. The base includes an increasing-thickness portion
formed so that the less the distance between a part of the
increasing-thickness portion and the ring-shaped wallsurrounding portion
is, the thicker the part of the increasing-thickness portion becomes.

[0013] Optional combinations of the aforementioned constituting elements
and implementations of the invention in the form of methods, apparatuses,
or systems may also be practiced as additional modes of the present
invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Embodiments will now be described, by way of example only, with
reference to the accompanying drawings, which are meant to be exemplary,
not limiting, and wherein like elements are numbered alike in several
figures, in which:

[0015] FIG. 1A shows a top view of the disk drive device according to an
embodiment;

[0016] FIG. 1B shows a side view of the disk drive device according to the
embodiment;

[0017]FIG. 1c shows a bottom view of the disk drive device according to
the embodiment;

[0018]FIG. 2 is a view that is sectioned along the line A-A, as
illustrated in FIG. 1A;

[0027]FIG. 8 shows a cross section of the disk drive device according to
a modification.

DETAILED DESCRIPTION OF THE INVENTION

[0028] The invention will now be described by reference to the preferred
embodiments This does not intend to limit the scope of the present
invention but to exemplify the invention. The size of the component in
each figure may be changed in order to aid understanding. Some of the
components in each figure may be omitted if they are not important for
explanation.

[0029] The disk drive device according to the embodiment of the present
invention is an example of a rotating device and is preferably used as a
hard disk drive that has a magnetic recording disk.

[0030] In the disk drive device according to the embodiment, the thickness
of the base gradually is increased as it gets close to a portion of the
base that surrounds and supports a bearing unit. This will improve the
impact resistance of the base.

[0031] (A Disk Drive Device 100)

[0032] FIG. 1A is a top view of the disk drive device 100 according to the
embodiment. In FIG. 1A, the disk drive device 100 is shown without a top
cover 2 in order to show the inside of the disk drive device 100. The
disk drive device 100 comprises: a base 4; a rotor 6; a magnetic
recording disk 8; a data read/write unit 10; and the top cover 2.

[0033] Hereinafter, it is assumed that the side of the base 4 on which the
rotor 6 is installed is the upper side.

[0034] The magnetic recording disk 8 is mounted on the rotor 6, and
rotates with the rotor 6. The rotor 6 is rotatably mounted to the base 4
through the bearing unit 12, which is not shown in FIG. 1A. The base 4 is
produced by die-casting an alloy of aluminum. The base 4 includes: a
bottom plate 4a forming the bottom portion of the disk drive device 100;
and an outer circumference wall 4b formed along the outer circumference
of the bottom plate 4a so that the outer circumference wall 4b surrounds
an installation region of the magnetic recording disk 8. Six screw holes
22 are formed on the upper surface 4c of the outer circumference wall 4b.

[0035] The data read/write unit 10 includes: a read/write head (not
shown); a swing arm 14; a voice coil motor 16; and a pivot assembly 18.
The read/write head is attached to the tip of the swing arm 14. The
read/write head records data onto and reads out data from the magnetic
recording disk 8. The pivot assembly 18 swingably supports the swing arm
14 with respect to the base 4 around the head rotation axis S. The voice
coil motor 16 swings the swing arm 14 around the head rotation axis S and
moves the read/write head to the desired position on the upper surface of
the magnetic recording disk 8. The voice coil motor 16 and the pivot
assembly 18 are constructed using a known technique for controlling the
position of the head.

[0036] FIG. 1B is a side view of the disk drive device 100 according to
the embodiment. The top cover 6 is fixed onto the upper surface 4c of the
outer circumference wall 4b of the base 4 using six screws 20. The six
screws 20 correspond to the six screw holes 22, respectively. In
particular, the top cover 2 and the upper surface 4c of the outer
circumference wall 4b are fixed together so that the joint portion
between both does not create a leak into the inside of the disk drive
device 100. The inside of the disk drive device 100, for example, is a
clean space 24 surrounded by the bottom plate 4a of the base 4 and the
outer circumference wall 4b of the base 4 and the top cover 2. This clean
space 24 is designed so that the clean space 24 is sealed, in other
words, there is neither leakage from the outside or to the outside. The
clean space 24 is filled with clean gas, with particles removed. This can
suppress adhesion of contaminants, such as particles, onto the magnetic
recording disk 8 and can increase the reliability of the disk drive
device 100.

[0037] The clean gas that is filled in the clean space 24 may, for
example, be air. Alternatively the clean gas may include, by a certain
ratio, a gas comprised of molecules of less molecular weight such as
Helium molecules (each of which is a monatomic molecule). Alternatively
the clean gas may be substantially pure Helium gas.

[0038] The rotating magnetic recording disk 8 tends to levitate due to
wind pressure caused by the rotation of the magnetic recording disk 8. In
the case where this buoyancy force is strong, in order to avoid touching,
it is necessary to design the disk drive device so that the gap between
the read/write head and the magnetic recording disk 8 is relatively wide.
However, in the case where the clean gas filled in the clean space 24
includes Helium gas, the less molecular weight of Helium may make the
wind pressure during the rotation of the magnetic recording disk 8
relatively small. Therefore, it would be possible to narrow the gap
between the read/write head and the magnetic recording disk 8, thereby
increasing the amount of recordable data per unit area of the magnetic
recording disk 8.

[0039] In principle, the lower limit of the gap between the read/write
head and the magnetic recording disk 8 corresponds to the size of the
molecule of the clean gas filled in the clean space 24. Therefore, the
fact that the clean gas includes relatively large amount of small
molecules may make it possible to further narrow the gap.

[0040]FIG. 1c is a bottom view of the disk drive device 100 according to
the embodiment. Referring to FIGS. 1A, 1B and 1C, for the purpose of
fixing a pin made of stainless steel or for the other purposes, a first
through hole 82a is formed in the bottom plate 4a of the base 4 and a
second through hole 82b is formed in the outer circumference wall 4b. A
pin is inserted into the first through hole 82a or the second through
hole 82b and mechanically is fixed there. In the case where the bottom
plate 4a or the outer circumference wall 4b is thinned in order to thin
or trim weight of the disk drive device 100, the amount of leakage
through the first through hole 82a or the second through hole 82b may be
increased. In particular, in the case where the clean gas filled in the
clean space 24 includes a great amount of Helium gas, the amount of
leakage may be larger than the case where the clean gas includes a great
amount of a gas of larger molecular weight. The large amount of leakage
would substantially change, for example within a period of time used
generally for aging tests, the total amount of the clean gas filled in
the clean space 24 or the ratio of Helium gas. If at least one of these
parameters changes, then the gap between the read/write head and the
magnetic recording disk 8 may change. This change of the gap may prevent
the reading/writing of data.

[0041] To cope with this, with regard to the lower surface 4k of the base
4, a first seal member 84a is provided along the edge of the first
through hole 82a. In particular, the first seal member 84a covers the
first through hole 82a. With regard to the side surface 4ba of the outer
circumference wall 4b, a second seal member 84b is provided along the
edge of the second through hole 82b. In particular, the second seal
member 84b covers the second through hole 82b. Each of the first and
second seal members 84a, 84b may be provided, for example, by forming a
sheet-like material including resin into a predetermined shape (for
example, a disk) and fixing it by a glue. This preferably may facilitate
the work. Alternatively, each of the first and second seal members 84a,
84b may be provided by applying hardening resin in liquid form and then
hardening the applied hardening resin using heat or UV radiation. This
preferably may suppress the removal of the seal member due to impact.

[0042] After providing the first seal member 84a or the second seal member
84b, an aging test may be performed. In this aging test, one checks the
change of the total amount of the clean gas filled in the clean space 24
or the change of the ratio of Helium gas, after a predetermined period of
time has passed. If, in this aging test, the amount of change with
respect to the device under test is found to be equal to or more than a
predetermined reference amount of change, the device under test may be
removed as a seal malfunction.

[0043] According to the above, the reliability of the disk drive device
100 may be increased.

[0044]FIG. 2 is a view that is sectioned along the line A-A, as
illustrated in FIG. 1A. The rotor 6 includes: a shaft 26; a hub 28; a
thrust ring 30; and a cylindrical magnet 32. The magnetic recording disk
8 is mounted on a disk-mount surface 28a of the hub 28. Three screw holes
34 for affixing a disk are arranged on the upper surface 28b of the hub
28 at 120-degree intervals around the rotational axis R of the rotor 6.
The clamper 36 is pressed against the upper surface 28b of the hub 28 by
three screws 38 for affixing a disk, which are screwed in the
corresponding three screw holes 34 for affixing a disk. The clamper 36
presses the magnetic recording disk 8 against the disk-mount surface 28a
of the hub 28.

[0045] The hub 28 is made of soft-magnetic steel such as SUS430F. The hub
28 is formed to be predetermined cup-like shape by, for example, the
press working or cutting of a steel plate. For example, the hub 28 may
preferably be made of the stainless steel (DHS1) provided by Daido Steel
Co., Ltd. since the stainless steel has lower outgas and is
easily-worked. The hub 28 may more preferably be made of the stainless
steel (DHS2) provided by Daido Steel Co., Ltd. since the stainless steel
has high corrosion resistance.

[0046] The shaft 26 is fixed in the hole 28c arranged at the center of the
hub 28 by using both press-fitting and glue, the hole 28c being arranged
coaxially with the rotational axis R of the rotor 6.

[0047] The thrust ring 30 is in ring-shape and has a reverse L-shaped
cross section. The thrust ring 30 is glued on an inner surface 28e of a
hanging portion 28d of the hub 28. The thrust ring 30 may be made of
steel such as SUS303 or SUS430F. The thrust ring 30 is formed by, for
example, the press working or cutting of a steel plate. For example, the
thrust ring 30 may preferably be made of the stainless steel (DHS1)
provided by Daido Steel Co., Ltd. since the stainless steel has lower
outgas and is easily-worked. The thrust ring 30 may more preferably be
made of the stainless steel (DHS2) provided by Daido Steel Co., Ltd.
since the stainless steel has high corrosion resistance.

[0048] In the case where the thrust ring 30 is made of steel that is
softer than the hub 28 (in particular, the hanging portion 28d), it is
more likely that the thrust ring 30 is deformed as it is attached to the
inner surface 28e of the hanging portion 28d. If the thrust ring 30 is
deformed, the gap between the thrust ring 30 and its surroundings may
become narrower than the one that is required. Therefore, the thrust ring
30 is made of steel the hardness of which substantially is equal to that
of the hub 28. This may suppress the deformation of the thrust ring 30.

[0049] The cylindrical magnet 32 is glued on a cylindrical inner surface
28f that is an inner cylindrical surface of the cup-like hub 28. The
cylindrical magnet 32 is made of a rare-earth material such as Neodymium,
Iron, or Boron. The cylindrical magnet 32 faces radially towards twelve
teeth of the laminated core 40. The cylindrical magnet 32 is magnetized
for driving, with sixteen poles along the circumferential direction. The
surface of the cylindrical magnet 32 is treated for preventing rusting by
electro deposition coating or spray coating.

[0050] The disk drive device 100 further comprises a bearing unit 12, a
laminated core 40, coils 42, and a suction plate 86. The base 4 rotatably
supports the hub 28 through the bearing unit 12. A ring-shaped wall 4e,
the center of which is along the rotational axis R of the rotor 6, is
formed on the upper surface 4d of the base 4. The ring-shaped wall 4e
protrudes upwardly and surrounds the bearing unit 12. An inner surface of
the ring-shaped wall 4e forms the bearing hole 4h in which the bearing
unit 12 is inserted and glued. The base 4 includes an
increasing-thickness portion 4n formed so that the less the distance
between a part of the increasing-thickness portion 4n and the ring-shaped
wall 4e is, the thicker the part of the increasing-thickness portion 4n
becomes. The upper side of the cross section of the increasing-thickness
portion 4n is formed to be a downwardly-convex smooth function or a
straight line.

[0051] The bearing unit 12 includes the housing 44 and the sleeve 46 and
rotatably supports the rotor 6 with respect to the base 4.

[0052] The housing 44 is glued in the bearing hole 4h of the base 4. The
housing 44 is formed to be cup-shaped by integrating a cylindrical
portion and a bottom portion as a single unit. The housing 44 is glued to
the base 4 with the bottom portion downside.

[0053] The cylindrical sleeve 46 is glued on the inner side surface of the
housing 44. A jetty portion 46a, which radially juts out, is formed at
the upper end of the sleeve 46. This jetty portion 46a, in cooperation
with the thrust ring 30, limits the motion of the rotor 6 in the
direction along the rotational axis R (hereinafter referred to as "axial
direction").

[0054] By making the housing 44 cup-shaped, a housing 44 with a higher
strength can be realized compared with the case where the cylindrical
portion and the bottom portion are formed separately and coupled
afterwards. In addition, the assembling can be made easier. In the case
where the cylindrical portion and the bottom portion are formed
separately and coupled afterwards, it would be difficult to decrease the
axial dimension of the housing since it is necessary to provide a region
for gluing in order to obtain predetermined glue strength. Therefore, by
making the housing 44 cup-shape, it would be possible to further thin the
housing 44.

[0055] The sleeve 46 accommodates the shaft 26. The lubricant 48 is
injected into a lubricant fill space 88 in between part of the rotor (the
shaft 26, the hub 28, and the thrust ring 30) and the bearing unit 12.
The lubricant fill space 88 includes: two groove portions 90a, 90b
corresponding to a pair of herringbone-shaped radial dynamic pressure
grooves 50 which are vertically separated from each other, the pair of
grooves 50 are formed on the inner surface of the sleeve 46; and a
non-groove portion 92 corresponding to the region between the two groove
portions 90a, 90b where there is no dynamic pressure groove.

[0056] The bearing unit 12 is formed so that each of the lengths, in the
axial direction, of the two groove portions 90a, 90b is greater than that
of the non-groove portion 92. In this case, the decrease of the radial
dynamic pressure in thinning the disk drive device 100 may be suppressed.

[0057] The groove portion 90a is the rotor-side one (upper one) of the two
groove portions 90a, 90b. The bearing unit 12 is formed so that the
length, in the axial direction, of the groove portion 90a is greater than
that of the other groove portion 90b. In this case, by making the length,
in the axial direction, of the groove portion 90a relatively greater, the
bearing stiffness there could relatively be increased. The groove portion
90a is closer to the rotor 6 and owes a larger radial load than that of
the other groove portion 90b. The disk drive device 100 according to the
embodiment is suitable for this kind of situation and can cope with the
radial load more efficiently.

[0058] A first herringbone-shaped or spiral-shaped thrust dynamic pressure
groove (not shown) is formed on the lower surface of the thrust ring 30
that faces the upper surface of the housing 44. A second
herringbone-shaped or spiral-shaped thrust dynamic pressure groove (not
shown) is formed on the upper surface of the thrust ring 30 that faces
the lower surface of the jetty portion 46a. The rotor 6 is axially and
radially supported by the dynamic pressure generated in the lubricant 48
by radial dynamic pressure grooves and thrust dynamic pressure grooves
when the rotor 6 rotates.

[0059] The pair of herringbone-shaped radial dynamic pressure grooves may
be formed on the shaft 26. The first thrust dynamic pressure groove can
be formed on the upper surface of the housing 44, and the second thrust
dynamic pressure groove may be formed on the lower surface of the jetty
portion 46a. Alternatively, the thrust dynamic pressure grooves may be
formed on a lower surface of the hub 28 that faces the jetty portion 46a
or the upper surface of the jetty portion 46a.

[0060] A capillary seal TS, where the gap between the inner surface 30c of
the thrust ring 30 and the outer surface 44a of housing 44 gradually
increases downward, is formed on the upside of the housing 44. The liquid
level, which is a boundary between the clean gas filled in the clean
space 24 and the lubricant 48, is located in the middle of the capillary
seal TS. The capillary seal TS forms an entrance to the lubricant fill
space 88. The capillary seal TS prevents the leakage of the lubricant 48
by way of the capillary effect. The inner surface 30c of the thrust ring
30 is formed so that the radius of the inner surface 30c decreases
axially downward. In this case, the centrifugal force associated with the
rotation of the rotor 6 applies the lubricant 48 a force directed towards
the inside of the lubricant 48.

[0061] The laminated core 40 has a ring portion and twelve teeth, which
extend radially outwardly from the ring portion, and is fixed on the
upper surface 4d side of the base 4. The laminated core 40 is formed by
laminating six thin magnetic steel sheets and mechanically integrating
them. An insulation coating is applied onto the surface of the laminated
core 40 by electrodeposition coating or powder coating. Each of the coils
42 is wound around one of the twelve teeth, respectively. A driving flux
is generated along the teeth by applying a three-phase sinusoidal driving
current through the coils 42.

[0062] The increasing-thickness portion 4n is thick on the coil 42 side.
Therefore, if no countermeasure is provided and an impact is applied to
the disk drive device, the increasing-thickness portion 4n may touch the
coil 42 and the insulation between them may not be maintained. To cope
with this, the coil 42 is formed so that the distance between the coil 42
and the increasing-thickness portion 4n is greater than a predetermined
distance such as 0.1 mm. That is, the minimum distance between the
increasing-thickness portion 4n and the coil 42 is equal to or greater
than 0.1 mm. This may decrease the probability that the
increasing-thickness portion 4n touch the coil 42 when an impact is
applied to the disk drive device 100.

[0063] In particular, the coil 42 has a decreasing-thickness portion 42a
the thickness of which decreases in accordance with the profile of the
increasing-thickness portion 4n. The decreasing-thickness portion 42a is
formed so that the less the distance between a part of the
decreasing-thickness portion 42a and the rotational axis R is, the
thinner the part of the decreasing-thickness portion 42a is. For example,
the decreasing-thickness portion 42a is formed by winding the coil 42
with the number of turns decreasing towards the rotational axis R.
Alternatively, the decreasing-thickness portion 42a is formed by
pressing, in a direction in which the thickness of the coil 42 is
measured, and thinning a part of the coil 42 that is close to the
rotational axis R.

[0064] The laminated core 40, through the central hole 40a of the ring
portion of the laminated core 40, is fitted to the outer surface 4g of
the ring-shaped wall 4e with a press-fit or clearance fit and glued
thereon. One example of how the laminated core 40 is fitted is that the
laminated core 40 is fixed at the position where the laminated core 40
surrounds a portion of the side surface of the bearing hole 4h, the
portion contacting the outer surface 44a of the housing 44. In this case,
by going through the process in which the bearing unit 12 is mounted on
the base 4 after the laminated core 40 is mounted on the base 4, the
ring-shaped wall 4e of the base 4 is radially fixed by the laminated core
40 when the bearing unit 12 is mounted. Therefore, the deformation of the
ring-shaped wall 4e associated with the insertion of the bearing unit 12
into the bearing hole 4h can be suppressed. As a result, the squareness
of the bearing unit 12 after insertion can be improved. In many cases,
the base 4 is made of aluminum, which is relatively soft metal. The
present embodiment may preferably used for the cases where the base 4 is
made of aluminum in particular.

[0065] The glued connection between the housing 44 and the base 4 is
further described below. A ring-shaped first groove 4j, the center of
which is along the rotational axis R of the rotor 6, is arranged on a
side surface of the bearing hole 4h of the base 4. The first groove 4j
has a semicircular cross section. A ring-shaped second groove 44b, the
center of which is along the rotational axis R, is arranged on an outer
surface 44a of the housing 44, the outer surface 44a contacting the side
surface of the bearing hole 4h. The position of the second groove 44b in
the axial direction is different from the position of the first groove 4j
in the axial direction. The second groove 44b has a semicircular cross
section.

[0066] Each of the first groove 4j and the second groove 44b may have a
polygonal cross section or semielliptical cross section or rounded cross
section.

[0067] The first groove 4j and the second groove 44b holdhave glue
therein.

[0068] The conductive resin 52 is applied on the edge portion 41 of the
bearing hole 4h on the lower surface 4k of the base 4. This conductive
resin 52 electrically connects the base 4 and the housing 44. A cut
portion 4m is arranged on the lower surface 4k of the base 4 by cutting
along the edge portion 41 of the bearing hole 4h. The width of the cut
portion 4m in the radial direction is greater than the depth of the cut
of the cut portion 4m. The conductive resin 52 is applied so that it
starts from the cut portion 4m and reaches the bottom surface 44c of the
housing 44. In particular, the conductive resin 52 is applied in the cut
portion 4m so that the height (the thickness in the axial direction) of
the conductive resin 52 is less than the depth of the cut of the cut
portion 4m.

[0069] Various materials can be adopted as the conductive resin 52. For
example, a so-called, two-component epoxy in which polyoxypropylene
diamine, as a hardener, is applied to a base resin, which is a mixture of
an epoxy resin and silver powder, is easy to apply, is strong, has
flexibility, and has good impact resistance. The two-component epoxy is
also preferable in that there is a less volatile portion.

[0070] Various types of glue can be adopted as the glue to glue the
housing 44 and the base 4. An anaerobic glue containing an acrylic acid
ester as a main ingredient is preferable in that it is easy to work with.
This anaerobic glue does not cure while it is exposed to air. Once the
anaerobic glue enters in a fitted portion between the housing 44 and the
base 4, the anaerobic glue rapidly reacts, polymerizes, and cures. By
this, one can obtain a first stage of strength within a short period of
time. In addition, since there is less contraction, the anaerobic glue is
preferably used as a sealant to prevent leaks at the fitted portion.
Furthermore, in the case where ultraviolet curability is given to the
anaerobic glue, it is preferable in that spilled-out glue can be cured
within a short period of time by irradiating ultraviolet light, thereby
the work piece can be made rapidly available to handle.

[0071] It is possible that the glue or the conductive resin 52 gradually
emits a volatile portion. This volatile portion may contaminate the clean
space 24 and may prevent normal data read/write operation. To cope with
this, the disk drive device 100 in assembly may be put in a
high-temperature container for a long period of time, after assuring the
electrical connection between the base 4 and the housing 44 by gluing the
base 4 and the bearing unit 12 using the glue and applying the conductive
resin 52, and before mounting the magnetic recording disk 8 onto the
rotor 6. This can accelerate the removal of the volatile portion of the
glue or the conductive resin 52. For example, by putting the disk drive
device 100 in the high-temperature container for more than one hour while
keeping the temperature of the high-temperature container higher than 65
degrees Celsius, most of the volatile portion of the glue or the
conductive resin 52 can be removed. By putting the disk drive device 100
in the high-temperature container for more than one hour while keeping
the temperature of the high-temperature container higher than 75 degrees
Celsius, a sufficient amount of the volatile portion of the glue 54 or
the conductive resin 52 can be removed. By keeping the temperature of the
high-temperature container lower than 100 degrees Celsius, it is possible
to prevent the glue or the conductive resin 52 from denaturing or being
weakened due to heat.

[0072]FIG. 3 shows a top view of the suction plate 86. The A-A line in
FIG. 3 corresponds to the cross section of FIG. 2. The suction plate 86
faces the cylindrical magnet 32 in the axial direction. The suction plate
86 is made of a magnetic material. The suction plate 86 has a ring
portion 86b and six projecting portions 86a that radially inwardly extend
from the ring portion 86b. The suction plate 86 is fixed to the base 4 by
six projecting portions 86a being fixed to the base 4 by, for example,
swaging. The suction plate 86 is attracted by the cylindrical magnet 32
since the suction plate 86 is made of the magnetic material. This applies
to the cylindrical magnet 32 a force downward in the axial direction,
thereby levitation of the rotor 6 while rotation of the rotor 6 is
suppressed.

[0073]FIG. 4 shows a magnified cross section around the thrust ring 30 of
the disk drive device 100 of FIG. 2. The thrust ring 30 has a hub-facing
surface that faces the hub 28 in the axial direction. The hub-facing
surface has an outer periphery region 30a and an inner periphery region
30b. The outer periphery region 30a touches a lower surface 28g of the
hub 28. The inner periphery region 30b has the second thrust dynamic
pressure grooves. The inner periphery region 30b rotates under the jetty
portion 46a.

[0074] In the case where the outer periphery region 30a and the inner
periphery region 30b are formed with different heights in the axial
direction, it would be difficult to improve the precision of the height
of the inner periphery region 30b in the axial direction. This is because
a manufacturing error of the lower surface 28g of the hub 28 and a
manufacturing error of the inner periphery region 30b and the outer
periphery region 30a adds together. If the precision of the height of the
inner periphery region 30b in the axial direction is low, a precision of
the gap between the inner periphery region 30b and the jetty portion 46a
would be low. If this precision of the gap is low, it would be necessary
to make this gap larger in order to prevent the two from touching, and
the thinning of the disk drive device may become difficult accordingly.

[0075] To cope with this, the outer periphery region 30a and the inner
periphery region 30b of the thrust ring 30 may be formed such that the
two are tangential to a planar surface that is perpendicular to the
rotational axis R. That is, the thrust ring 30 may be formed so that the
hub-facing surface substantially is planar. In this case, the outer
periphery region 30a and the inner periphery region 30b are coplanar in
the axial direction, and the inner periphery region 30b is located at the
same position in the axial direction with the lower surface 28g of the
hub 28. As a result, the precision of the height in the axial direction
of the inner periphery region 30b can be kept high.

[0076] The length L3, in the axial direction, of the lubricant 48 existing
in the capillary seal TS relates to the length L1, in the axial
direction, of the bearing hole 4h such that making one of the two longer
results in making the other shorter. In the case where the dimension
(thickness), in the axial direction, of the disk drive device 100 should
be constant, making the length L2, in the axial direction, of the hanging
portion 28d longer results in making the length L1, in the axial
direction, of the bearing hole 4h shorter.

[0077] It may be possible to make the length L3, in the axial direction,
of the lubricant 48 longer than the length L1, in the axial direction, of
the bearing hole 4h. Alternatively, it may be possible to make the length
L2, in the axial direction, of the hanging portion 28d longer than the
length L1, in the axial direction, of the bearing hole 4h. However, a
short length L1, in the axial direction, of the bearing hole 4h may
promote the peel-off of the glued portion between the bearing unit 12 and
the base 4 when an impact is applied to the disk drive device 100. If the
peel-off of the glued portion happens, a disk drive device having an
arrangement with narrow gaps may experience a problem such as touching.
To cope with this, the disk drive device 100 may be arranged so that the
length L1, in the axial direction, of the bearing hole 4h is longer than
the length L3, in the axial direction, of the lubricant 48 existing in
the capillary seal TS. Also, the disk drive device 100 may be arranged so
that the length L1, in the axial direction, of the bearing hole 4h is
longer than the length L2, in the axial direction, of the hanging portion
28d. In these cases, the impact resistance of the glued portion between
the bearing unit 12 and the base 4 can be improved.

[0078]FIG. 5 shows a magnified cross section of the left half of FIG. 2.
In FIG. 5, the rotational axis R is defined to be a z axis. It is assumed
that the z coordinate of the lower surface 4k of the base 4 is z=0.

[0079] The portion where the housing 44 touches the ring-shaped wall 4e
occupies a range of z0<z<z2 in the z coordinate. The
laminated core 40 occupies a range of <z1<z<z3 in the
z coordinate. Here, the disk drive device 100 is arranged so that
z0<z1<z2<z3 holds, in other words the range
of the z coordinate of the portion where the housing 44 touches the
ring-shaped wall 4e at least partly overlaps the range of the z
coordinate of the laminated core 40. In this case, it is possible to
obtain a large portion where the housing 44 touches the ring-shaped wall
4e, thereby the impact resistance of the glued portion between the
bearing unit 12 and the base 4 can be improved.

[0080] The suction plate 86 occupies a range of z4<z<z6 in
the z coordinate. The hub 28 occupies a range of z5<z<z7
in the z coordinate. Here, the disk drive device 100 is arranged so that
z4<z5<z6<z7 holds, in other words the range
of the z coordinate of the suction plate 86 at least partly overlaps the
range of the z coordinate of the hub 28. Accordingly, a labyrinth
structure is arranged by the suction plate 86 and the magnet mount
portion 28h of the hub 28, the labyrinth structure being arranged between
an inner space of the hub 28 and the outer space of the hub 28. In this
case, even if unintendedextraneous substance such as droplets of
lubricant 48 exists in the inner space of the hub 28, the spread-out of
such extraneous substance to the outside of the hub 28 may be suppressed
due to the labyrinth structure.

[0081] The inner surface of the ring-shaped wall 4e forms part of the side
surface of the bearing hole 4h. A ring convex portion 4r is provided on
the ring-shaped wall 4e, the ring convex portion 4r further protruding
towards the hub 28 side. An outer surface of the ring convex portion 4r
is fit to the ring portion of the laminated core 40. The hanging portion
28d and the thrust ring 30 rotate in the region defined partly by the
ring convex portion 4r on the rotational axis R side.

[0082] The increasing-thickness portion 4n is arranged radially outwardly
of the ring convex portion 4r and is formed so that the thickness
increases towards the ring convex portion 4r. The coil-facing portion 4p
is arranged to be adjacent to the increasing-thickness portion 4n, which
is located outside of the increasing-thickness portion 4n in a radial
manner. The coil-facing portion 4p is arranged so that the thickness H0
substantially is constant. The thickness H0 is less than the half of the
length L1, in the axial direction, of the bearing hole 4h. A surface of
the increasing-thickness portion 4n on the hub 28 side smoothly connects
to a surface of the coil-facing portion 4p on the hub 28 side.

[0083] It is possible to make the thickness H0 of the coil-facing portion
4p less than 0.7 mm. This is preferred since the disk drive device 100
can be thinned. As the thickness H0 of the coil-facing portion 4p is
decreased, the possibility that a pinhole is created in the aluminum
die-casting process or in the cutting process may increase. Therefore,
the thickness H0 of the coil-facing portion 4p may be made larger
than or equal to 0.4 mm. This is preferred since the creation of the
pinhole may be suppressed.

[0084] In FIG. 5, an x axis is defined along a straight line that is
perpendicular to the rotational axis R and that intersects with the
rotational axis R. The x coordinate of the rotational axis R is defined
to be x=0.

[0085] The increasing-thickness portion 4n is formed so that the following
equation is satisfied:

H ( x ) H 0 = 1.25 ( x x 0 ) - 1.2 (
equation 1 ) ##EQU00001##

[0086] where x denotes an x coordinate of a certain position in the
increasing-thickness portion 4n, x0 is the x coordinate of the
position in the increasing-thickness portion 4n that is the closest to
the rotational axis R, and H(x) is a thickness at the position x of the
increasing-thickness portion 4n. All of x, x0, H(x), H0 are in
the same unit such as mm.

[0087] For example, H0=0.7 mm, x0=4.8 mm,
H1=H(x0)=0.88 mm, (the x coordinate x1 of the outer most
position, in the radial direction, of the increasing-thickness portion
4n)=5.8 mm.

[0088] A portion of the hub 28 that faces the coil 42 in the axial
direction and a coil facing portion 4p of the base 4 that faces the coil
42 in the axial direction are considered below. In order to thin the disk
drive device 100, it would be one option to thin the portion of the hub
28 that faces the coil 42 in the axial direction. However, the inventors
have realized that, in this case, the magnetic recording disk 8 is more
susceptible to a vibration when the magnetic recording disk 8 is mounted
and rotated with high speed compared with the case where the coil-facing
portion 4p is thinned. Therefore, in the disk drive device 100, the
portion of the hub 28 that faces the coil 42 in the axial direction is
thicker than the coil-facing portion 4p. In other words, (the thickness
H2 of the portion of the hub 28 that faces the coil 42 in the axial
direction)>H0.

[0089] The operation of the disk drive device 100 as described above shall
be described below. The three-phase driving current is supplied to the
coils 42 to rotate the magnetic recording disk 8. The driving fluxes are
generated along the twelve teeth by making the driving current flow
through the coils 42. These driving fluxes give torque to the cylindrical
magnet 32, and the rotor 6 and the magnetic recording disk 8, which is
fitted to the rotor 6, rotate. Along with this, the voice coil motor 16
swings the swing arm 14, and the read/write head goes back and forth
within the swing range on the magnetic recording disk 8. The read/write
head converts magnetic data recorded on the magnetic recording disk 8 to
an electrical signal and transmits the electrical signal to a control
board (not shown). The read/write head also converts data sent from the
control board in a form of an electrical signal to magnetic data and
writes the magnetic data on the magnetic recording disk 8.

[0090] When the disk drive device 100 is thinned, it may be one option to
make the base 4 thin rather than the hub 28 in light of the vibration
during rotation as described above. One of the points to be kept in mind
when thinning the base 4 is impact resistance. When acceleration due to
an impact is applied to the disk drive device 100, a stress is applied
near the center of the base 4. The strength of the stress corresponds to
the value given by multiplying the acceleration due to the impact by sum
of the masses of the magnetic recording disk 8, the hub 28, the bearing
unit 12, the laminated core 40, and the coils 42. In particular, this
stress tends to concentrate at the boundary between the ring-shaped wall
4e and the increasing-thickness portion 4n.

[0091] In the case where no increasing-thickness portion 4n is provided
and a coil-facing portion of constant thickness is provided from the
ring-shaped wall 4e and is arranged to adjoin the ring-shaped wall 4e, a
stress due to an impact basically is distributed in the coil-facing
portion so that the stress is inversely proportional to the distance from
the rotational axis R. Therefore, the stress is concentrated at the
boundary between the ring-shaped wall 4e and the coil-facing portion, in
particular at the corner portion, and a plastic deformation or a crack
may be created therefrom.

[0092] In the disk drive device 100 according to the present embodiment,
the increasing-thickness portion 4n is formed so that the less the
distance between a part of the increasing-thickness portion 4n and the
ring-shaped wall 4e is, the thicker the part of the increasing-thickness
portion 4n is. Therefore, the stress at the boundary between the
ring-shaped wall 4e and the increasing-thickness portion 4n spreads and
the boundary can bear a larger stress in total. In other words, it is
possible to have the stress distributed substantially evenly,
independently of the distance from the rotational axis R. As a result,
the disk drive device 100 can bear a larger impact.

[0093] Alternatively, it is possible to thin the base 4 in response to the
improvement of the impact resistance caused by the increasing-thickness
portion 4n. Therefore, it may be possible to make the disk drive device
100 thinner.

[0094] The inventors of the present invention repeated simulations of
stress distribution by changing the shape of the increasing-thickness
portion 4n. According to these simulations, the inventors have found
that, in the case where the thickness H0 of the coil-facing portion
4p is in the range from 0.5 mm to 1.2 mm and the x coordinate x0 of
the position in the increasing-thickness portion 4n that is the closest
to the rotational axis R is in the range from 4 mm to 15 mm and the
increasing-thickness portion 4n is formed so that the following equation
is satisfied, the stress spreads out in a suitable manner and the stress
does not exceed, in simulations, the elastic limit of the material of the
base and the deformation of the base is kept within a range allowable for
real usage.

H ( x ) H 0 ≧ k ( x x 0 ) - 1.2 (
equation 2 ) ##EQU00002##

[0095] k is a constant determined by mechanical strength of the material
of the base. k may be determined by experiments.

[0096] In this simulation, the base is chosen to be an aluminum die-cast
(ADC12 in JIS). In this case, the tensile strength is about 300 MPa.
However, according to the experiences the inventors as skilled artisan
have, it is likely that a stress of about 150 MPa may already create a
deformation of about 0.2 percent. Therefore, preferably the stress is
suppressed below about 120 MPa. In the case where the base is made by
aluminum die-casting, the base may have a so-called blow hole that is a
low-density region. If the stress in the region where the blow hole
exists exceeds 150 MPa, the base may be largely deformed. Therefore, it
is more preferable that the stress is suppressed below about 100 MPa.
Using these criteria, the inventors have found that, in the case where an
upward acceleration due to an impact of 11760 m/s2 (1200 G) is
applied to the disk drive device and the base is made of Aluminum, the
threshold value was give by k=1.25. That is, the disk drive device that
satisfies the equation 2 above for k=1.25 can maintain the predetermined
height of the hub when the disk drive device receives a test impact load
of 1200 G.

[0097] FIGS. 6A, 6B and 6C show stress distributions obtained by
simulations, using contour lines. The simulations used here are computer
simulations in which finite element method is used. FIG. 6A shows the
results of the simulations in which the base does not have the
increasing-thickness portion 4n. As shown in FIG. 6A, in the case where
the base does not have the increasing-thickness portion 4n, the contour
lines are dense at the corner 200 of the base and the stress is
concentrated there. In particular, there is a region 202 near the corner
200 where the stress exceeds 180 MPa. Around there, there are wide
regions 204 where the stress exceeds 150 MPa. If a blow hole exists in
the regions 204 where the stress exceeds 150 MPa, the base may be largely
deformed.

[0098]FIG. 6B shows the results of the simulations in which the
increasing-thickness portion 4n is formed so that the following equation
is satisfied.

H ( x ) 0.7 = 1.25 ( x 4.8 ) - 1.2 (
equation 3 ) ##EQU00003##

[0099] In FIG. 6B, even the region 206 where the stress is the highest has
the stress of about 100 MPa. Therefore, it can be said that the stress is
suitably spread out in this shape of the increasing-thickness portion 4n.

[0100] FIG. 6C shows the results of the simulations in which the
increasing-thickness portion 4n is formed so that the following equation
is satisfied.

H(x)=5.92-0.9x (equation 4)

[0101] In FIG. 6C, the increasing-thickness portion 4n is thicker than
that shown in FIG. 6B. Therefore, the stress is further spread out and
the maximum stress is about 80 MPa. Therefore, even if the blow hole
exists, the deformation there can be suppressed.

[0102] In the design of a disk drive device, it is desired that a
sufficient torque is obtained even if the disk drive device is thinned.
In order to suppress the decrease of the torque by thinning, the usual
way is to make the cylindrical magnet 32 relatively thick. In order to
make the cylindrical magnet 32 relatively thick, it would be one option
to thin a suction plate accordingly. However, in the case where the
suction plate is fixed to the base 4 by evenly applying load to the whole
inner periphery of the suction plate, thinning of the suction plate may
make it more probable that even a slight unevenness of the swage load
applied to the inner periphery causes a large deformation of the suction
plate. If the suction plate is deformed, it may be difficult to keep the
gap between the suction plate and the cylindrical magnet 32 uniform along
the circumferential direction. If this gap becomes non-uniform, the
attracting force between the suction plate and the cylindrical magnet 32
changes in the circumferential direction. This may make the rotation of
the rotor 6 unstable. In the worst case, the suction plate may touch the
cylindrical magnet 32. According to the experiences the inventors as
skilled artisan have, in order to avoid this situation in the case where
the suction plate is fixed to the base 4 by evenly applying load to the
whole inner periphery of the suction plate, it is not advised in general
to make the thickness of the suction plate less than or equal to 0.5 mm.

[0103] To cope with this, in the disk drive device according to this
embodiment, the suction plate 86 has a ring portion 86b and six
projecting portions 86a that radially inwardly extend from the ring
portion 86b. The suction plate 86 is fixed to the base 4 by six
projecting portions 86a being fixed to the base 4 by, for example,
swaging. Here, load is applied to each of the six projecting portions
86a. Therefore, the suction plate 86 is less susceptible to deformation
than the case where a suction plate is fixed to the base 4 by evenly
applying load to the whole inner periphery of the suction plate. In
addition, the suction plate 86 can be further thinned and the cylindrical
magnet 32 can be made thicker accordingly, thereby increasing torque. In
particular, in the disk drive device 100 according to the present
embodiment, it is possible to make the thickness of the suction plate 86
less than or equal to 0.5 mm, or preferably less than or equal to 0.4 mm.

[0104] If the suction plate 86 is thinned too much, the suction plate
tends to be magnetically saturated and it may be difficult to maintain a
predetermined strength of an attraction force. To cope with this, the
thickness of the suction plate 86 may be made greater than or equal to
0.1 mm. This is advantageous because the predetermined strength of the
attraction force can be maintained. The suction plate 86 with the
thickness in the range from 0.2 mm to 0.3 mm is preferred since the
deformation can be suppressed as well as a stable attraction force is
realized.

[0105] In the present embodiment, referring to FIG. 5, the dimensions
along the straight line that is parallel to the rotational axis R and
that intersects the body of the suction plate 86 are as follows:

[0106] the thickness L1 of the hub 28=1.5 mm,

[0107] the thickness L2 of the cylindrical magnet 32=2.0 mm, the width L3
of the gap between the cylindrical magnet 32 and the suction plate
86=0.38 mm,

[0108] the thickness L4 of the suction plate 86=0.25 mm,

[0109] the thickness L5 of the base 4=0.7 mm, and

[0110] the thickness of the disk drive device 100=4.83 mm.

[0111] In the case where the thickness L4 of the suction plate 86 is
designed to be 0.4 mm, the thickness L2 of the cylindrical magnet 32 is
1.85 mm.

[0112] If the number of the projecting portions 86a is small, the suction
plate 86 may be fixed atilt. Therefore, the number of the projecting
portions 86a may be made greater than or equal to 3. This may reduce the
possibility of the suction plate 86 being fixed atilt. If the number of
the projecting portions 86a is large, the unevenness of the load applied
to the projecting portions 86a may cause deformation. Therefore, the
number of the projecting portions 86a may be made less than or equal to
12. This may suppress the deformation.

[0113] In the disk drive device 100 according to the present embodiment,
the first groove 4j and the second groove 44b both of which are filled
with glue serve to keep glue therein. Therefore, the glue strength
between the base 4 and the bearing unit 12 is improved. In addition,
these grooves improve the airtightness.

[0114] (A Manufacturing Method)

[0115] A method for manufacturing the disk drive device 100 according to
the embodiment will be described below. The shaft 26, the hub 28, the
thrust ring 30, the bearing unit 12 and the lubricant 48 are hereinafter
referred to as a fluid dynamic bearing.

[0116] In a bearing assembling step, the fluid dynamic bearing without the
lubricant 48 is assembled.

[0117] In a preparation step, a fluid dynamic bearing without the
lubricant 48 is placed in a work space that is able to be evacuated. The
fluid dynamic bearing is oriented so that the entrance of the capillary
seal TS faces up. Then the working pressure, which is a pressure in the
work space, is lowered to, for example, below 100 Pa and the lubricant
fill space 88 is depressurized.

[0118] In a injection step, a discharge nozzle for discharging the
lubricant 48 is inserted into the inside of the entrance of the capillary
seal TS. During this insertion, the discharge nozzle first moves to a
horizontal position corresponding to the entrance and then moves, in a
vertical direction, into the inside of the entrance. By doing so, when
the fluid dynamic bearing without the lubricant 48 is set in the work
space, the discharge nozzle is not an obstacle for the fluid dynamic
bearing. As a result, it is possible to easily set the fluid dynamic
bearing within a short period of time.

[0119] After inserting the discharge nozzle into the inside of the
entrance of the capillary seal TS, the lubricant 48 is discharged from
the discharge nozzle. The amount of the lubricant 48 that is discharged
is set so that the lubricant 48 does not spill out of the capillary seal
48. For example, the amount of the lubricant 48 that is discharged is set
so that the lubricant 48 fills up the capillary seal TS.

[0120] In a pull-in step, the pressure of the work space is restored to
the pressure such as the atmospheric pressure which is higher than the
pressure inside the lubricant fill space 88. The lubricant 48 is pulled
in to the inside of the lubricant fill space 88 by a pressure difference
between the inside and outside of the lubricant fill space 88. As a
result, the lubricant 48 is filled in the lubricant fill space 88.

[0121] In this pull-in step, gas such as air may remain in the lubricant
48 that is filled in the fluid dynamic bearing. If much air remains in
the fluid dynamic bearing, when the fluid dynamic bearing is put in a
low-pressure and high-temperature environment, the remaining air may
expand and the expanded air may push the lubricant 48 out of the bearing
unit 12 and may induce release of the lubricant 48. If the lubricant 48
spreads out, the reliability of the disk drive device may be
deteriorated. To cope with this, the present manufacturing method
includes a remaining gas inspection step, in which, after the pull-in
step, a fluid dynamic bearing is detected and removed as a defective unit
if the amount of air remaining in the lubricant 48 filled in the fluid
dynamic bearing is more than a predetermined amount. In this case, with
regard to a disk drive device manufactured by going through such an
inspection step, it is less likely that the lubricant 48 spills out due
to the remaining air.

[0122] The remaining gas inspection step includes a first measuring step
and a second measuring step and a removal step.

[0123] FIGS. 7A and 7B explain the measuring steps. FIG. 7A explains the
first measuring step. In the first measuring step, with regard to the
fluid dynamic bearing with the introduced lubricant 48, a second height
h2 of the liquid level 48a of the lubricant 48 in the direction
along the rotational axis R under a second pressure such as 1013 hPa (1
atmosphere) is measured with reference to the lower surface of the thrust
ring 30. FIG. 7A shows the situation where a remaining air 94 exists in
the upper part of the capillary seal TS.

[0124]FIG. 7B explains the second measuring step. In the second measuring
step, with regard to the fluid dynamic bearing with the introduced
lubricant 48, a first height h1 of the liquid level 48a of the lubricant
48 in the direction along the rotational axis R under a first pressure
such as 30 Pa which is lower than the second pressure is measured with
reference to the lower surface of the thrust ring 30. The first pressure
is lower than 100 Pa and preferably is in the range from 30 Pa to 50 Pa.
Since the first pressure is lower than the second pressure, the remaining
air 94 expands more than the case shown in FIG. 7A. The liquid level 48a
of the lubricant 48 moves downward accordingly and the first height h1
decreases.

[0125] In the removal step, a fluid dynamic bearing with the introduced
lubricant 48 is inspected based on the measured first height h1 and
the measured second height h2. In particular, if the absolute value
of the difference between the first height h1 and the second height
h2 is greater than a predetermined reference value, then the fluid
dynamic bearing is treated as the one that does not satisfy the criteria.
If a fluid dynamic bearing is judged as not satisfying the criteria, then
the fluid dynamic bearing is removed.

[0126] According to this remaining gas inspection step, an effect due to
the remaining gas can be detected with high precision. For example, if
the difference (h2-h1) between the first height h1 and the
second height h2 exceeds 50 μm, then the fluid dynamic bearing
may be removed as a defective unit.

[0127] In a stator assembling step, after the remaining gas inspection
step, the laminated core 40 with the coils 42 wound is fixed to the base
4. Then the bearing unit 12 of the fluid dynamic bearing is glued in the
bearing hole 4h of the base 4.

[0128] In a high-temperature step, after the bearing unit 12 is glued, the
assembly is put in a high-temperature container having clean atmosphere
at 65 to 100 Celsius degrees, for 1 to 3 hours. In the case where the
first seal member 84a and the second seal member 84b are hardening resin
in liquid form, the hardening resin may be applied in any one of the
steps before the high-temperature step. This is advantageous because the
high-temperature step may accelerate the hardening. In the case where the
first seal member 84a and the second seal member 84b are formed by fixing
a sheet-like material, the fixation may be performed after the
high-temperature step. This may prevent the seal member from
deteriorating.

[0129] In a disk assembling step, the magnetic recording disk 8, the data
read/write unit 10, etc. are mounted to the assembly. In the disk
assembling step, the top cover 2 is fixed to the upper surface 4c of the
outer circumference wall 4b of the base 4 using the screws 20. A clean
gas is filled in the clean space 24 through an opening of the base 4.
Afterwards, the opening is plugged using a predetermined plugging member.
Afterwards, a predetermined performance test step is performed on the
disk drive device 100 and the resultant is the manufactured disk drive
device.

[0130] Above is an explanation based on the exemplary embodiments. These
embodiments are intended to be illustrative only, and it will be obvious
to those skilled in the art that various modifications to constituting
elements and processes could be developed and that such modifications are
also within the scope of the present invention.

[0131] The embodiment describes the case where the coil 42 has a
decreasing-thickness portion 42a the thickness of which decreases in
accordance with the profile of the increasing-thickness portion 4n.
However, the present invention is not limited to this. For example,
instead of providing the decreasing-thickness portion 42a to the coil 42,
the increasing-thickness portion may be formed so that the distance
between the coil and the increasing-thickness portion is greater than a
predetermined distance such as 0.1 mm. This may also decrease the
probability that the increasing-thickness portion touch the coil when an
impact is applied to the disk drive device.

[0132] The embodiment describes the case where the suction plate 86 has a
ring portion 86b and six projecting portions 86a that radially inwardly
extend from the ring portion 86b. However, the present invention is not
limited to this. For example, the suction plate may have a ring portion
and a plurality of projecting portions that radially outwardly extend
from the ring portion. In this case, the suction plate is fixed to the
base 4 by the plurality of projecting portions being fixed to the base 4
by, for example, swaging.

[0133] The embodiment describes the case where the housing 44 is formed to
be cup-shaped by integrating the cylindrical portion and the bottom
portion as a single unit. However, the present invention is not limited
to this. For example, the housing may be formed so that the diameter of
the portion where the housing touches the ring-shaped wall is greater
than the diameter of other portion.

[0134]FIG. 8 shows a cross section of the disk drive device 300 according
to a modification. The housing 44' is formed so that, in the bearing
unit, the diameter D1 of the portion where the housing 44' touches the
bearing hole 4' h of the base 4' is greater than the diameter D2 of the
other portion(for example, such as the diameter D2 of the upper part of
the housing 44'). The base 4' is formed so that the diameter of the
bearing hole 4' h is greater than the diameter of the thrust ring 30.

[0135] According to this modification, the area of glued portion between
the housing 44' and the base 4' is greater than that of the embodiment.
Therefore, the glue strength is strengthened.

[0136] The embodiment describes the so-called outer-rotor type of the disk
drive device 100 in which the cylindrical magnet 32 is located outside
the laminated core 40. However, the present invention is not limited to
this. For example, the present invention may be applied to the so-called
inner-rotor type of the disk drive device in which the cylindrical magnet
is located inside the laminated core.

[0137] The embodiment describes the case where the bearing unit 12 is
fixed to the base 4, and the shaft 26 rotates with respect to the bearing
unit 12. However, the present invention is not limited to this. For
example, the present invention may be applied to a shaft-fixed type of
the disk drive device in which the shaft is fixed to the base, and the
bearing unit and the hub rotate together with respect to the shaft.

[0138] The embodiment describes the case where the bearing unit 12 is
directly mounted onto the base 4. However, the present invention is not
limited to this. For example, a brushless motor comprising a rotor, a
bearing unit, a laminated core, coils, and a base can separately be
manufactured, and the manufactured brushless motor can be installed on a
chassis.

[0139] The embodiment describes the case where the laminated core is used.
However, the present invention is not limited to this. The core does not
have to be a laminated core.

[0140] The embodiment describes the case where the housing 44 and the
sleeve 46 are separate parts. However, the present invention is not
limited to this. For example, the housing and the sleeve can be made as a
single unit. In this case, the number of parts can be reduced, and it may
become easier to assemble.

[0141] While the preferred embodiments of the present invention have been
described using specific terms, such description is for illustrative
purposes only, and it is to be understood that changes and variations may
be made without departing from the spirit or scope of the appended
claims.